Locking synchronizing means for transmission shifts

ABSTRACT

A locking synchronizer for transmission shifts, has a sliding sleeve carrier and a gear revolving at different speeds of rotation coupled together upon attaining synchronism via an axially slidable, annular sliding sleeve. A coupling tooth array of the sliding sleeve engages a corresponding spur gearing of the sliding sleeve carrier as well as a coupling tooth array of the gear, with engagement pins positioned between the sliding sleeve carrier and sliding sleeve. Portions of the gear form with portions of the synchronizing ring a coupling capable of transmitting force and with locking teeth on the synchronizing ring for the temporary prevention of the axial movement of the sliding sleeve, whereby the preventive action is cancelled even during existing difference in speed of rotation as a function of the warming on the synchronizing ring or a defined unlocking force which acts transversely to the motion of the sliding sleeve on the locking teeth of the synchronizing ring.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of Ser. No. 07/272,773 filed Aug. 26, 1988 (U.S. Pat. No. 4,964,505) as a national phase application of PCT/EP87/00142 filed Mar. 11, 1987 and based, in turn, upon the Luxembourg application PCT/EP86/00166 filed Mar. 21, 1986, under the International Convention.

FIELD OF THE INVENTION

This invention relates to a locking synchronizing means for transmission shafts.

BACKGROUND OF THE INVENTION

Synchronizing means are known from Looman-Zahnradgetriebe (Konstruktionsbucherband 26) Springer-Verlag Berlin/Heidelberg/New York 1970, page 259, FIG. 10.9, where the clutching tooth array of the sliding sleeve is locked onto the locking tooth array of the synchronizing ring as long as synchronism is not achieved between the synchronizing body and the gear. Such arrangements are very advantageous for the driver, because they require relatively little attention to shifting. However, they have the disadvantage that the friction means are overlooked due to the appearance of large differences in speed of rotation and the high shifting forces frequently applied, and therefore wear out rapidly and fail prematurely. Particularly when shifting into reverse while the vehicle still moves ahead, relatively high differential speeds of rotation have to be synchronized, so that the synchronizing means are especially endangered for such a shift.

However, the engine is also in jeopardy since, in a locking synchronizing arrangement, the engagement of the reverse gear cannot be excluded with certainty during excessively fast forward motion. Upon clutching-in, the engine can be damaged because of reversal of rotation.

OBJECT OF THE INVENTION

It is the object of the invention to fashion a synchronizing means such that overloading and thereby a destruction of the synchronizing means and damage to the engine is prevented.

This object is attained with locking synchronizing means for transmission shifting, in which a carrier for sliding sleeve and a gear rotating at a different speed of rotation are coupled together rigidly at synchronism by means of an axially slidable annular sliding sleeve. A coupling tooth array of the sliding sleeve engages a corresponding spur gearing of the sliding sleeve carrier and the coupling tooth array of the gear as well. Engagement pins are positioned between the sliding sleeve carrier and sliding sleeve and in an uncoupled condition, engage in a recess of the interior of the sliding sleeve and have pressure surfaces which are in effective connection with pressure surfaces on a synchronizing ring. The latter which is positioned axially between the sliding sleeve carrier and the gear, and is capable of being entrained by the sliding sleeve carrier circumferentially, with play, in both directions, via dogs. Portions of the gear together with portions of the synchronizing ring form a power-transmitting coupling system having friction surfaces and with locking teeth on the synchronizing ring for the temporary lockout of the axial motion of the sliding sleeve.

According to the invention, the locking action of the locking teeth is limited even during prevailing difference in speed of rotation and is cancelled as a function of the warming of the synchronizing ring or by an increase of the unlocking force and/or a reduction of the friction moment. Grinding noises are generated upon axial motion of the sliding sleeve in the direction toward the coupling tooth array during a prevailing excessive difference in speed of rotation. These grinding noises cause the driver to complete the shifting operation only after applying means of synchronizing speed of rotation.

An overloading of the synchronizing means is prevented with certainty by doing away with the locking action in the face of a prevailing differential speed of rotation between the elements to be connected, namely the sleeve and gear. If this achieved by warming of the synchronizing ring, then the latter expands and detaches itself from the friction cone of the gear because it bears axially against the gear. The friction moment on the cone collapses, and due to the effect of the unlocking force from the axial force of the sliding sleeve on the locking tooth of the synchronizing ring the latter is turned backwards, and the sliding sleeve can be moved in axial direction further upon upon the array of coupling teeth of the gear. A like effect is also obtained by attuning the friction moment to the maximum unlocking force attainable. A sufficiently large unlocking force can overcome the friction moment even without the latter being nullified, and can turn the synchronizing ring backward in peripheral direction, so that the locking teeth of synchronizing ring cannot prevent the axial movement of the sliding sleeve any lower. With such an arrangement, normal, or is permissible shifts are handled even in reverse gear, without a destruction of synchronization due to overload becoming possible. If however the forward motion and thus the differential speed of rotation between sliding sleeve and gear is still too fast, then a grinding or rattling noise will be caused by the attempted engagement of the spur gear teeth of the sliding sleeve with the coupling tooth array of the gear, so that the driver will not complete at all or well delay shifting. This prevents damage to the engine due to reversal of rotation.

The synchronizing ring can be so dimensioned that when the difference of speed of rotation between the gear and the sliding sleeve carrier and the sliding sleeve is too high, it is heated up due to an excessively long duration of friction, it expands and bears against the face of the coupling tooth array, and thus the friction on the friction surfaces is cancelled. Alternatively, the locking surfaces and the locking teeth of the synchronizing ring and on the sliding sleeve are so dimensioned angularly, that the possible unlocking force (p) which results from the axial shifting force (PS) of the shifting sleeve, is greater than the friction moment (R) resulting from the friction pair of the friction surfaces. The friction surfaces between synchronizing ring and gear can have a profile which reduces the friction surface or a conformation lowering the friction value. The cone angle α of the friction surfaces can be made especially great, e.g. above 10°.

The signal to the driver can be made very perceptible by an appropriate fashioning of the faces of the coupling tooth array, e.g. by proper rounding, so that a damage to the engine can be prevented with even greater assurance. If the axial distance between the synchronizing ring and its bearing against the face of the coupling tooth array is held small, and is so adjusted that the heat, generated when synchronization is attempted while vehicle speed is too high, will cause expansion of the synchronizing ring, and its bearing against the face, then due to the collapse of the friction moment the locking action between the sliding sleeve and the locking tooth on the synchronizing ring is nullified, and the sliding sleeve can be move in an axial direction onto the coupling tooth array of the gear. If a difference in rotational speed remains, then a grinding noise will be caused, and the shift, e.g. into reverse, can be further delayed, until the difference in rotation permits a faultless shift.

The adjustment of the unlocking force and of the friction moment can be attained by appropriate shaping of the angles for the locking surfaces on the sliding sleeve and the synchronizing ring for reduction of the unlocking force or by appropriate shaping or the angles of the friction cones or their friction surface for reduction of the friction moment.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features and advantages of my invention will become more readily apparent from the following description, reference being made to the accompanying highly diagrammatic drawing in which:

FIG. 1 is a cross sectional view of a double shift coupling with synchronizing means;

FIG. 2 is a partial section of FIG. 1 through a gear and a synchronizing ring; and

FIG. 3 is a schematic representation of the locking surface on the coupling tooth array of the sliding sleeve and the gear as well as the locking tooth array of the synchronizing ring.

SPECIFIC DESCRIPTION

FIG. 1 shows a double shift coupling with locking synchronizing means. For simplicity, however, only one locking synchronizing means is described in one shift coupling. On a drive shaft 6 is fastened a carrier fastened a carrier 1 for a sliding sleeve 3. The carrier is fixed against rotation and axial movement, axial movement relative to shaft 6, and is connected to the sliding sleeve 3, via gear tooth array 11, 31. The sliding sleeve 3 is thus fixed against rotation relative to the carrier 1 and shaft 6.

Additionally, a synchronizing ring 5 is provided. The ring 5 has a conical friction surface 52 located between the carrier 1 for the sliding sleeve 3 and the gear 2. This friction surface 52 cooperates with the friction surface 22 of gear 2. Additionally, several engagement pins or pressure bolts 4 are distributed along the circumference of sliding sleeve carrier 1 and which are urged radially outwardly compression springs 41 into conical recesses of sliding sleeve 3. The radially outward portion is shaped as a spherical surface or is fashioned as a ball in known manner. The synchronizing ring 5 is connected to the carrier 1 for sliding sleeve 3 in known manner via an arrangement of dogs, whereby a relative motion in circumferential direction as well as an axial motion is possible. The friction surface 22 coordinated to gear 2 is formed directly on gear 2 or on a coupling body fastened on the gear. The gear proper of the coupling body carries additionally a coupling tooth array 21, which is rounded or chamfered off in axial direction, that is toward the sliding sleeve. In the partial view of FIG. 2, synchronizing ring 5 is shown in addition to gear 2. The friction surfaces 22 of the gear and 52 of the synchronizing ring form the conical friction means with the cone angle α. The axial distance between gear 2 and the synchronizing ring is designated with A.

FIG. 3 shows in schematic representation a tooth 31 of the sliding sleeve 3 with the locking surface 33 and a locking tooth 51 of the synchronizing ring 5 with the locking surface 53. The unlocking force acting on locking tooth 51 is designated P, which results from the shifting force PS which acts on the sliding sleeve and the angle of the locking surfaces 33, 53. The friction moment R counteracts the unlocking force in circumferential direction.

The sliding sleeve 3 entrains engagement pins when moved in the directions of the arrows shown, e.g. to the left, and the engagement pins press upon the respective (i.e. left-hand) synchronizing ring so as to initiate synchronization (i.e. angular movement of the ring with the shaft).

The synchronizing ring moves slightly axially in the same direction as the sliding sleeve. The friction arrangement 52, 22 between gear and synchronizing ring becomes active, and the synchronizing ring is moved in circumferential direction by a limited amount so that a further axial movement of the sliding sleeve this is prevented from further axial movement via the locking teeth 51 on the synchronizing ring and the locking surfaces 53 and 33, in accordance with FIG. 3 (for the left-hand ring). The locking teeth 51 of the synchronizing ring 5 are, in this case held in this locking position by the friction moment. While a normal locking synchronization is held in this position for the length of time until synchronization is attained between gear 2 and sliding sleeve carrier 1 or the sliding sleeve 3, respectively, the friction moment is negated when difference of speed of rotation still prevails, or the unlocking force, while shifting force PS is fully effective, is greater than the friction moment, so that the synchronizing ring 5 is turned backwards via the locking surfaces 33, 53, and the sliding sleeve can be moved further in axial direction.

The reduction or even cancellation of the friction moment can be attained by a suitable dimensioning of the synchronizing ring, so that it heats up and expands when the difference in rotational speed is too large. If in this case the gap between gear 2 and synchronizing ring 5, according to FIG. 2, is relatively small, then the synchronizing ring will come to abut against the gear on its face and breaks away with friction surface 52 from the friction surface 22 of the gear. The friction moment R collapses, and the sliding sleeve 3 can be slid further in direction toward gear 2. If the difference in rotational speed is still too high, then there will be grinding (noise) upon engagement of the tooth tops of the sliding sleeve 3 with coupling tooth array 21 of gear 2, so that the operator can discontinue the operation without allowing the driver to destroy synchronization. The ratio between unlocking force to friction moment can thereby be influenced by the angle on the locking surfaces 33, 53 of the locking surfaces 33, 53 of the coupling tooth array 31 and the locking tooth array 51, because the unlocking force is increased by a steeper angle. A further effect is possible by reduction of the friction moment. This can be accomplished by reduction of the physical size of the friction surface by a suitable choice of its profile. The friction moment can also be reduced by an appropriate cone angle of about 10° or more, since the cone angle in a conventional synchronization device is about 6°. 

We claim:
 1. In a locking synchronizing device for a gearshift system in which a sliding sleeve support and a gearwheel, which rotate at different speeds, are positively coupled together when in synchronism by means of an axially displaceable annular sliding sleeve, a synchro-mesh tooth system of the sliding sleeve meshing with a respective external tooth system of the sliding sleeve support and the synchro-mesh tooth system of the gearwheel, with thrust bolts, which are arranged between the sliding sleeve support and the sliding sleeve, engage in the uncoupled state in a recess at the inside of the sliding sleeve and comprise thrust surfaces which are operatively connected to thrust surfaces on a synchronizing ring, which is arranged axially between the sliding sleeve support and the gearwheel and is connected with circumferential play to the sliding sleeve support so as to be driven in both circumferential directions, parts of a gearwheel forming with parts of the synchronizing ring a frictional coupling having friction surfaces and with locking teeth on the synchronizing ring for temporarily stopping the axial movement of the sliding sleeve, the improvement wherein, if there is still a speed differential between the gearwheel and the sliding sleeve support, the locking effect of the locking teeth is limited, so that when the sliding sleeve moves axially the locking teeth on the synchronizing ring are turned in the circumferential direction with respect to the sliding sleeve support by the synchro-mesh tooth system of the sliding sleeve, the locking effect being limited by a reduction in the frictional moment due to the synchronizing ring heating up and a taper of the friction surfaces, so that when the sliding sleeve moves axially in the direction of the gearwheel the contact between the two synchro-mesh tooth systems give rise to chattering noises which cause the driver to refrain from completing the gearshift operation until the speeds are equal.
 2. The locking synchronizing device according to claim 1, wherein the cross section of the synchronizing ring is so formed that it heats up considerably as a result of an excessive friction period and thus expands and the friction at the friction surfaces is counteracted.
 3. The locking synchronizing device according to claim 1 wherein the locking surfaces at the locking teeth of the synchronizing ring and the sliding teeth are pointed to an extent such that an unlocking moment, which results from an axial shift force of the operating sleeve, is greater than a frictional moment from friction pairing of the friction surfaces.
 4. The locking synchronzing device according to claim 1 wherein the friction surfaces between the synchronizing ring and the gearwheel are of a form, due to their cone angle or profiling, which reduces the coefficient of friction.
 5. The locking synchronizing device according to claim 1 wherein the cone angle of the friction surfaces is distinctly greater than 6°. 